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0620 s03 Qp 6 Model Answers Final

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Centre Number

Candidate Number

Name

CAMBRIDGE INTERNATIONAL EXAMINATIONS International General Certificate of Secondary Education

CHEMISTRYPaper 6 Alternative to Practical

0620/06May/June 2003 1 hour

Candidates answer on the Question Paper. No additional materials required.

READ THESE INSTRUCTIONS FIRST Write your name, Centre number and candidate number at the top of this page. Write in dark blue or black pen in the spaces provided on the Question Paper. You may use a pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions. The number of marks is given in brackets [ ] at the end of each question or part question.

For Examiners Use 1 2 3 If you have been given a label, look at the details. If any details are incorrect or missing, please fill in your correct details in the space given at the top of this page. Stick your personal label here, if provided. 4 5 6 TOTAL

This document consists of 12 printed pages.SP (SM) S33031/3 CIE 2003

[Turn over

2 1 Look at the diagrams of common laboratory apparatus.

For Examiners Use

mortarA

[I]

stirrer or stirring rod

[I]

B

C

tripod

[I]

D

bunsen burner

[I]

0620/06/M/J/03

3 (a) Complete the empty boxes to identify the pieces of apparatus labelled. (b) What name is given to the separation method in C? [4]

For Examiners Use

filtration ......................................................................................................................................[1](c) Which apparatus would be most suitable to obtain crystals from an aqueous solution of copper(II) sulphate?

D or describe process - liquid is evaporated to obtain crystals ......................................................................................................................................[1]2 A student carried out an experiment to investigate the speed of the reaction between sodium thiosulphate and dilute hydrochloric acid. Na2S2O3 + 2HCl 2NaCl + S + H2O + SO2 Experiment 1 By using a measuring cylinder, 50 cm3 of sodium thiosulphate solution was poured into a 100 cm3 beaker. The beaker was placed on a cross drawn on a piece of paper. 10 cm3 of hydrochloric acid was added to the beaker and the timer started. eye

10 cm3 of hydrochloric acid

beaker

aqueous sodium thiosulphate

paper with cross marked on it The time was taken until the cross could not be seen. The time was recorded in the table.

0620/06/M/J/03

[Turn over

4 Experiments 2, 3, 4 and 5 Experiment 1 was repeated using different volumes of sodium thiosulphate as shown in the table. All experiments were carried out at 25 C. Table of results volume of sodium thiosulphate/cm3 50 40 30 20 10 volume of water/cm3 0 10 20 30 40 time for cross to disappear/s 45 60 80 130 255

For Examiners Use

Experiment 1 2 3 4 5

(a) Why does the cross on the paper disappear?

the solution goes cloudy or turbid because a precipitate forms of sulphur ................................................................................................................................................................................................................................................................................[2] (b) Why was the total volume of solution kept constant?

fair test because the beaker will contain the same depth of mixture ................................................................................................................................................................................................................................................................................[1] (c) In which order should the water, hydrochloric acid and sodium thiosulphate solution be added to the beaker?

sodium thiosulphate first ...................................................................................................................................water second ..............................................................................................................................acid last ................................................................................................................................[1]

0620/06/M/J/03

5 (d) (i) Plot the results on the grid below. Draw a smooth line graph and label it 25 C. [5] 50

For Examiners Use

40

30

volume of sodium thiosulphate / cm3

50C

25C

20

10

0

50

100

150 time / s

200

250

300

(ii)

Sketch on the grid the graph you would expect if the experiments were repeated at 50 C. Label this graph. [2]

0620/06/M/J/03

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6 (e) The experiments were repeated using a 250 cm3 beaker instead of a 100 cm3 beaker. Suggest how the results would differ. Explain your answer.

For Examiners Use

same volume in each beaker ..........................................................................................................................................

I00cm3

250cm3

Answer

the time will be longer [I] because the depth of liquid is less so the ..........................................................................................................................................reaction time will need to produce more sulphur to obscure the cross ................................................................................................................................................................................................................................................................................[2]

3

A student investigated the redox reaction between potassium iodate(V) and iodide ions. Two experiments were carried out. Experiment 1 A burette was filled up to the 0.0 cm3 mark with the solution A of sodium thiosulphate. By using a measuring cylinder, a 10 cm3 sample of the solution B of potassium iodate(V) was added into a conical flask. A 10 cm3 sample of dilute sulphuric acid was added to the flask followed by 20 cm3 of aqueous potassium iodide. Solution A was added slowly to the flask until there was a pale yellow colour in the contents of the flask. Starch solution was then added into the flask and the colour changed to blueblack. Solution A was added to the flask until the colour just disappeared. Use the burette diagram to record the volume in the table. final burette reading / cm316 17 18

Experiment 2 Experiment 1 was repeated using solution C of potassium iodate(V) instead of solution B. Use the burette diagrams to record the volumes in the table and complete the table. initial burette reading / cm3 16 final burette reading / cm3 24

17

25

18

26

0620/06/M/J/03

7 Table of results Burette readings/cm3 Experiment 1 Final reading Initial reading Difference Experiment 2

For Examiners Use

I7.2 [I]0.0

24.5

[I] [I][4]

I6.97.6

I7.2

[I]

The reaction of the mixture of potassium iodate(V), sulphuric acid and potassium iodide in the flask produces iodine. Sodium thiosulphate then reacts with the iodine. (a) (i) In which Experiment was the greatest volume of aqueous sodium thiosulphate used?

Experiment I ...............................................................................................................................[1](ii) Compare the volumes of sodium thiosulphate used in Experiments 1 and 2.

In experiment I more than twice the volume in experiment 2 ..................................................................................................................................................................................................................................................................[1] (iii) Suggest an explanation for the difference in the volumes.

Solution B was more than twice the concentration of solution C. ..................................................................................................................................................................................................................................................................[2] (iv) Predict the volume of solution A which would be needed to react completely if Experiment 1 was repeated with 20.0 cm3 of the solution of potassium iodate. Explain your prediction.

[I]

I7.2 x 2 = 34.4 cm volume of solution A .................................................................................................using twice the volume of potassium iodate produces twice explanation ...............................................................................................................

3

[2]

amount of iodine, which in turn will need twice the volume of ...............................................................................................................................[3](b) Suggest the reason starch solution was added.

thiosulphate

I indicator 2 easier to see 3 makes titration more accurate .................................................................................................................................................................................................................................................................................... ......................................................................................................................................[2]

[2]

0620/06/M/J/03

[Turn over

8 4 A mixture of two solid compounds D and E was analysed. Solid D was a zinc salt which is soluble in water. Solid E was an insoluble metal carbonate. The tests on the mixture and some of the observations are in the following table. Complete the observations in the table. tests (a) About half of the mixture of D and E was placed in a test-tube. The mixture was heated (b) The rest of the mixture of D and E was added to distilled water in a boiling tube. The contents of the tube were filtered. The filtrate and the residue were kept for the following tests. test on residue (c) The residue was transferred from the filter paper in to a test-tube. About 3 cm3 of dilute sulphuric acid was added. The gas was tested with limewater. observations

For Examiners Use

green to black suggest copper(II ) condensation formed water given

compounds off

From above D is a soluble zinc salt. It will dissolve and be the filtrate. E will be the insoluble metal carbonate - the residue

bubbles, fizzing or effervescence ........................................................................ limewater goes milky ............................................................................................................................................[2]

[I][I]

The solution obtained in (c) was divided into two equal portions. (d) (i) To the first portion was added excess aqueous sodium hydroxide, a little at a time. To the second portion was added excess aqueous ammonia, a little at a time.

pale blue precipitate

(ii)

[I]

blue precipitate ........................................................................deep blue or royal blue solution ............................................................................................................................................[4]

[I]

[I]

0620/06/M/J/03

9 tests test on filtrate (e) The filtrate from (b) was divided into three approximately equal portions. (i) To the first portion were added drops of aqueous sodium hydroxide, a little at a time with shaking. observations

For Examiners Use

white precipitate ............................................................................................................................................[2]

[I]

[I]

Excess aqueous sodium hydroxide was added. (ii) To the second portion was added excess aqueous ammonia a little at a time.

dissolves to a colourless solution ....................................................................[1]

[I]

white precipitate ........................................................................dissolves to a colourless solution ............................................................................................................................................[3]

[I]

[I]

[I]

(iii)

To the third portion were added drops of dilute hydrochloric acid and aqueous barium chloride.

white precipitate

(f)

What conclusions can you draw about the identity of solid D?

D is hydrated [I] (zinc) sulphate [I] ................................................................................................................................................................................................................................................................................[2] (g) What conclusions can you draw about the identity of the cation in solid E?

Copper only ..........................................................................................................................................

[I]

but Cu ......................................................................................................................................[2]

2+

[2]

0620/06/M/J/03

[Turn over

10 5 An experiment was carried out using the apparatus below.

For Examiners Use

20

40

60

80

100 cm3

rubber connector

reaction mixture

By using a measuring cylinder, 20 cm3 of hydrogen peroxide was placed in the flask and 0.8 g of the catalyst, manganese(IV) oxide was added. The bung was replaced and the gas collected was measured at 1 minute intervals. The results were plotted on the grid (opposite). (a) (i) (ii) Draw a smooth line graph on the grid. Which result appears to be inaccurate? Why have you chosen this result? [1]

Result at 5 min ................................................................................................................................... Not on curve or gas has escaped or misreading of syringe ...............................................................................................................................[2](b) What mass of manganese(IV) oxide would remain at the end of the experiment?

[I]

[I]

0.8g ......................................................................................................................................[1](c) What would be the effect of using a rubber connector with a hole in it?

[I] [I] Volumes lower ......................................................................................................................................[2]

Leak, loss of gas ..........................................................................................................................................

0620/06/M/J/03

11 160

140

[I]

120

100 volume of gas / cm3 80

60

40

20

0

1

2

3

4 time / minutes

5

6

7

8

0620/06/M/J/03

[Turn over

12 6 Beach sand is a mixture of sand and broken shells (calcium carbonate). Calcium carbonate reacts with dilute hydrochloric acid to form a solution of calcium chloride. Plan an investigation to find out the percentage of shell material in a given sample of beach sand.

For Examiners Use

I. known mass of dry beach sand ...................................................................................................................................................2. Add excess ..................................................................................................................................................

3. of dilute hydrochloric acid ..................................................................................................................................................4. Filter to remove sand from solution of calcium chloride ..................................................................................................................................................

5. Wash to remove traces of solution ..................................................................................................................................................

6. Dry residue (sand) ..................................................................................................................................................7. Weigh sand ..................................................................................................................................................

8. % shell = Mass of beach sand - mass of residue x I00% ..............................................................................................................................................[6]Mass of beach sand

0620/06/M/J/03

Summary of Comments on IGCSE Chemistry Paper 6 June 2003Page: 2Q1 Q1 A Q1 B You are asked the name of the labelled piece of apparatus not the process the container is the mortar and the other part is the pestle Not thermometer, if a thermometer is drawn the bulb is shaded black to indicate that it contains mercury remember you are not asked the name of the process - filtration - but the name of piece of apparatus Give full name and do not use words such as 'heat'

Q1 C

Q1 D

Page: 3Q2 Q2 Sulphur, which is insoluble in water, is formed look at this diagram, it will help you to answer (c)

Page: 4Q2 (a) Q2 (c) The solution goes cloudy, this has to be explained Once the acid and thiosulphate are mixed the reaction starts and so must the timing. It is not important which goes in first water or thiosulphate - but the acid must be last. The volume of thiosulphate varies from experiment to experiment, and is generally larger than volume of acid which is always 10 cm.

Page: 5Q2 (d) i All points plotted correctly [3] -1 for each incorrect point Smooth line [1] label [1]

Q2 (d) iQ2 (d) i

This line is an indicative sketch, not a definitive plot .each small square on the x axis is 5s

Page: 6Q2 (e) In the bigger beaker the surface area will be greater so the depth will be less Hint - 0.0 is at top of burette helps with answer to (b) You must remember that the scale on a burette reads DOWN so this is 17.2 NOT 18.8 cm

Q3 Q3 Q3

Page: 7Q3 Q3 (a) ii Q3 (a) iii Q3 (a) iv Q3 (a) iv Q3 (b) this line is important, needed to answer a(iv) Usually in question of this type, volume will be in a simple ratio 2:1 Examiners expect more than simple conclusion the line of text above (a)(i) is relevant to answering this part Do not forget units When most of the iodine has reacted the colour is a pale yellow but when starch is added it goes to an intense blue black. The thiosulphate is added until it just goes colourless - all iodine has reacted. Very accurate. any two

Q3 (b)

Page: 8Q4 Q4 (a) Q4 (d) Reaction of cations must be learned Both (a) and blue precipitate shows a copper(II) salt Both (a) and blue precipitate shows a copper(II) salt

Page: 9Q4 (e) Q4 (e) iii you are told that it is a zinc salt. So reaction of cations again This is the test for a sulphate

Page: 10Q5 Q5 (a) ii See (b) An acceptable answer is that some gas has escaped and this was marked as correct. However if gas has escaped between 4 - 5 minutes all subsequent readings would be lower. The most probable/best explanation is that the volume of gas in the syringe was not read correctly it is the catalyst - alters rate but chemically unchanged

Q5 (b)

Page: 11Q5 (a) i you are asked in a(i) to draw a smooth curve

is not a smooth curve

Page: 12Q6 Q6 Sand does not react and remains as a solid Any six of above

of 16/16
This document consists of 12 printed pages. SP (SM) S33031/3 © CIE 2003 [Turn over CAMBRIDGE INTERNATIONAL EXAMINATIONS International General Certificate of Secondary Education CHEMISTRY 0620/06 Paper 6 Alternative to Practical May/June 2003 1 hour Candidates answer on the Question Paper. No additional materials required. READ THESE INSTRUCTIONS FIRST Write your name, Centre number and candidate number at the top of this page. Write in dark blue or black pen in the spaces provided on the Question Paper. You may use a pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions. The number of marks is given in brackets [ ] at the end of each question or part question. Centre Number Candidate Number Name If you have been given a label, look at the details. If any details are incorrect or missing, please fill in your correct details in the space given at the top of this page. Stick your personal label here, if provided. For Examiner’s Use 1 2 3 4 5 6 TOTAL
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